Curtain walls typically include a plurality of glazing panels (windows made of glass or plastic) supported in a framework of vertical and horizontal structural elements. Some known curtain walls utilize shear blocks to attach a horizontal structural element (mullion) to a vertical structural element (mullion), e.g., a curtain wall manufactured by Kawneer/Alcoa of Norcross, Ga. known as 1600 has such features. Shear blocks can roll/twist if the weight of the glazing unit or other load supported by the horizontal mullion exceeds the capacity of the shear blocks, causing the integrity of the curtain wall/glazing unit to be compromised. This may happen, e.g., if a curtain wall designed for single glazed glazing panels or double glazing is fitted with triple glazed glazing panels or if an overload is placed on the mullion through accident or misuse.
Another attribute of curtain walls is that they are increasingly being used as a support for installed devices and structures, such as sunshades, light shelves, canopies, etc. These devices may be attached with brackets and fasteners, such as screws, to a surface of the horizontal or vertical members of a curtain wall, e.g., the front face of a mullion. The weight of such installed devices must be controlled so as not to exceed the pullout values of the fasteners extending into the curtain wall. In addition, if a given device is removed or repositioned, the mounting holes used by the fasteners remain in the curtain wall surface compromising the appearance and integrity of the curtain wall.
The devices installed on curtain walls include those that use or generate electricity and therefore have attendant wiring to and from associated circuits inside and/or outside the building on which the curtain wall is present. For example, signage, power generating devices, such as solar panels, power generating windmills, sunshades and light shelves may be attached to a curtain wall façade. In addition, buildings increasingly utilize sensors, lighting devices, surveillance and communication devices, such as antennas, that require associated wiring. Wiring on, in or through a curtain wall presents challenges, in that drilling through mullions weakens them and degrades weather intrusion resistance. The wiring or electrical conduit is unsightly and it is difficult to route wiring through the interior hollows of curtain walls, as this typically requires pushing or pulling wire through elongated hidden channels, which may have constrictions and hidden obstacles. The wiring of devices mounted on or near a curtain wall is typically done after installation of the device to be wired. Once installed on, in or through a curtain wall, it is difficult to trace a specific wire to remove or replace it. Alternative curtain wall systems therefore remain desirable.